One of the goals of plant genetic engineering is to produce plants with agronomically important characteristics or traits. Recent advances in genetic engineering have provided the requisite tools to transform plants to contain and express foreign genes (Kahl et al. (1995) World Journal of Microbiology and Biotechnology 11:449-460). Particularly desirable traits or qualities of interest for plant genetic engineering would include, but are not limited to, resistance to insects and other pests and disease-causing agents, tolerances to herbicides, enhanced stability, yield, or shelf-life, environmental tolerances, and nutritional enhancements. The technological advances in plant transformation and regeneration have enabled researchers to take pieces of DNA, such as a gene or genes and incorporate the exogenous DNA into the plant's genome. The gene or gene(s) can then be expressed in the plant cell to exhibit the added characteristic(s) or trait(s).
Promoters are regulatory elements that play an integral part in the overall expression of a gene or gene(s). It is advantageous to have a variety of promoters to tailor gene expression such that a gene or gene(s) is transcribed efficiently at the correct time during plant growth and development, in a location in the plant, and/or in the amount necessary to produce the desired effect. In one case, for example, constitutive expression of a gene product may be beneficial in one location of the plant, but less beneficial in another part of the plant. In other cases, it may be beneficial to have a gene product produced at a certain developmental stage of the plant, or in response to certain environmental or chemical stimuli. The commercial development of genetically improved germplasm has also advanced to the stage of introducing multiple traits into crop plants, also known as a gene stacking approach. In this approach, multiple genes conferring different characteristics of interest can be introduced into a plant. It is important when introducing multiple genes into a plant, that each gene is modulated or controlled for expression and that the regulatory elements are diverse, to reduce the potential of gene silencing which can be caused by processes including but not limited to recombination or methylation of homologous sequences. In light of these and other considerations, it is apparent that control of gene expression and regulatory element diversity are important in plant biotechnology.
Therefore a need exists for promoters that have been shown to direct the transcription of genes during stressful conditions. A promoter that upregulates endogenous gene expression when the plant within which it resides was placed in a stressful condition could be used to drive heterologous genes from a number of different pathways, including but not limited to signaling molecules, transcription factors, or enzymes that could provide tolerance to the stresses that induced transcription from the endogenous promoter, or other genes. This upregulation of genes could lead to better yield through enhancement of the transgenic plant's tolerance for stress.